Detectives believe one of the men served as a lookout in the small gallery room, she said. Investigators also are looking at fingerprints on the display case, but they may be of visitors unconnected to the heist.

The bar was recovered by treasure hunter Mel Fisher and his crew in 1980 from the shipwreck of the Santa Margarita, which sank 25 miles west of Key West. The Santa Margarita is the sister ship of the storied galleon Atocha, also worked by Fisher.

Between them, the vessels carried 250,000 silver coins, according to the museum. They went down during a storm.

Crean said the case has generated a lot of interest. "Mel Fisher was such a dream builder," she said.

The museum's insurance company has offered a $10,000 reward for the return of the 16.5-karat gold bar, which weighs 74.85 ounces. The uniqueness of the piece places the bar's value at $550,000, Kendrick said.

"Having the money [insurance] in its place would not be a winner for me," Kendrick told CNN on Thursday night.

Fisher, who died in 1998, loved having the bar in a special reach-in case because it allowed visitors to make a connection with the find, Kendrick said.

The director said the bar, if recovered, will be returned to the case -- with a few security modifications.

Police said the modern-day pirates might find it difficult to sell the gold bar.